Ultraviolet A radiation transiently disrupts gap junctional communication in human keratinocytes

Abstract

2002.-Ultraviolet A (UVA) (320-400 nm) radiation is known to cause cutaneous aging and skin cancer. We studied the effect of UVA (365 nm) radiation on the human epidermis by focusing on keratinocyte gap junction-mediated intercellular communication (GJIC). We observed a dose-dependent 10-fold decrease in GJIC induced by UVA in normal human keratinocytes. This decrease in GJIC was associated with time-dependent internalization of connexin43 (Cx43). UVA radiation also damaged the actin cytoskeleton, as shown by microfilament disappearance. Importantly, the decrease in GJIC was transient when keratinocytes were irradiated with 10 J/cm 2 UVA, with a return to baseline values after 8 h. Concomitantly, Cx43 was relocalized and the actin cytoskeleton was restored. UVA irradiation and 12-O-tetradecanoylphorbol 13-acetate (TPA) treatment activated protein kinase C and reduced GJIC. However, Cx43 localization and phosphorylation were differently regulated by the two treatments. This suggests that at least two different pathways may mediate the observed fall in GJIC. These findings identify keratinocyte GJIC as a new UVA target that might sensitize human skin to photoaging and cancer formation.GJIC; connexin43; skin physiology; actin cytoskeleton; photoaging ULTRAVIOLET (UV) radiation is an energy source for life on earth that also has detrimental effects on animal life. The UV spectrum of solar radiation that reaches the earth's surface comprises UVB (280-320 nm) and UVA (320-400 nm). UVA has deleterious effects on the human epidermis by generating reactive oxygen species that can degrade lipids, proteins, and DNA and give rise to photo-oxidized products (26). The resulting oxidative stress can damage cellular components and change the pattern of gene expression, leading to photoaging and serious skin diseases such as cancer (20).The human epidermis is a multilayered, cohesive tissue with a unique functional architecture. It forms the primary barrier to the outside environment. Keratinocytes are the main component of the epidermis. Cells from the basal layer proliferate and then differentiate in the upper epidermal layer, where they acquire new biological properties. The symbiotic equilibrium between cell growth and differentiation in the epidermis points to an intimate spatial relationship in this tissue (31). Cell-cell communication via gap junctions appears to participate in epidermal homeostasis.Cell-cell communication occurs in the epidermal and dermal compartments of normal fully differentiated human skin. In the epidermis, gap junction-mediated intercellular communication (GJIC) usually involves groups of about a dozen keratinocytes (25). Gap junctions are clustered at cell-cell contacts and participate in local information share between cells. Each cell contributes a hemichannel (connexon) composed of six connexin (Cx) subunits that cross the plasma membrane four times and have their NH 2 and COOH termini in the cytoplasm (6). Gap junctions permit direct exchanges and sharing of ions and small molecules (Ն1,000 Da...

Ultraviolet A exposure induces reversible disruption of gap junction intercellular communication in lens epithelial cells

“…We also demonstrated that this UVA-induced reduction was reversible at a dose of 10 J/cm 2 . Our findings are consistent with previous studies (20). Inhibition of GJIc by UVA-irradiation has been reported to be associated with the deleterious effects of UVA on the human epidermis by generating ROS and compromising membrane stability (19).…”

“…Previous studies have shown that GJIc is a novel UVA target, and UVA-irradiation can disrupt the function of GJIc in human keratinocytes via p38 MAPK activation (19,20). UVA can induce various pathological changes in the lens epithelium.…”

“…In our study, we found a decrease in cx43 at both the mRNA and protein levels and an increase in PKc activity induced by UVA, suggesting that through PKc-activated cx phosphrylation, UVA may promote the degradation of cx43 and result in a decrease in intercellular communication. Gap junction has been reported as a new target of UVA-irradiation in the epidermis (19,20). The gap junction can be regulated by cx43 phosphorylation and dephosphorylation.…”

“…ROS was measured by flow cytometry using the ROS detection kit (Beyotime). Lipid peroxidation due to UVA-irradiation was measured as previously described (20). Briefly, SRA01/04 cells were plated in 60-mm petri dishes, 10 6 cells/dish, and incubated at 37˚C overnight.…”

“…UV and several kinases, include protein kinase c (PKc), mitogen-activated protein kinase (MAPK) and casein kinase (cK) I and II have been found to regulate cx43 phosphorylation, thus affecting the function of gap junction channels (18)(19)(20). Therefore, research on the UVA-induced phosphorylation of cx43 and its relationship to the lens gap junction, as well as the effect of non-lethal UVA on the lens epithelial cells is of great significance.…”